This invention relates to the field of retroreflectors, and more particularly, to lateral transfer retroreflectors.
Retroreflectors generally have the property of causing incident and reflected light rays to travel along parallel paths. To achieve this parallelism, a retroreflector normally consists of three optically flat reflecting surfaces, each reflecting surface positioned at a right angle to each of the other reflecting surfaces. Any departure of the reflecting surfaces from their perpendicular orientation will cause the incident and reflected light rays to depart from parallel.
Retroreflectors lose accuracy when they are exposed to external stresses. Examples of such external stresses are mass, thermal expansion or contraction of the substrate material from which the retroreflector is made, or deflection caused by curing of the adhesives which join members of the retroreflector.
Retroreflectors, and lateral transfer retroreflectors, which translate the reflected beam some calculated distance from the incident light beam, are old in the art. Examples of prior art retroreflectors and lateral transfer retroreflectors are:
U.S. Pat. No. 3,977,765, to Morton S. Lipkins, which discloses a retroreflector mounted to a support structure through means of applying an adhesive into the joints formed between joined members of the retroreflector and to a flat surface of the support structure.
U.S. Pat. No. 4,065,204, also to Morton S. Lipkins, which discloses a lateral transfer retroreflector consisting of a base, a roof reflector having two reflecting plates and a third reflector. The base acts as an extension of the third reflector by attaching the third reflector to the roof reflector in the manner known to retroreflectors to produce the lateral transfer retroreflector construction.
U.S. Pat. No. 5,024,514, to Zvi Bleier and Morton S. Lipkins, which discloses a lateral transfer retroreflector having a tubular member, a roof mirror and a mirror panel. Both the roof mirror and mirror panel are attached to the tubular member by use of three co-planar mounting pads.
It would be desirable to provide a high-accuracy lateral transfer retroreflector which, due to the construction of the tubular member and the manner of mounting the roof mirror to the tubular member, achieves reduced structural dimensions, less distortion due to mass and a more secure roof mirror mount.